Date: Tue, 4 Jun 2024 08:42:57 +0000
From: SkyLake Huang (黃啟澤)
	<SkyLake.Huang@...iatek.com>
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	<daniel@...rotopia.org>
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	<angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH net-next v6 5/5] net: phy: add driver for built-in 2.5G
 ethernet PHY on MT7988

On Mon, 2024-06-03 at 19:30 +0100, Russell King (Oracle) wrote:
>  	 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
>  On Mon, Jun 03, 2024 at 06:00:49PM +0100, Daniel Golle wrote:
> > On Mon, Jun 03, 2024 at 04:47:28PM +0100, Russell King (Oracle)
> wrote:
> > > On Mon, Jun 03, 2024 at 03:52:19PM +0100, Daniel Golle wrote:
> > > > On Mon, Jun 03, 2024 at 02:41:44PM +0100, Russell King (Oracle)
> wrote:
> > > > > On Mon, Jun 03, 2024 at 02:31:46PM +0100, Daniel Golle wrote:
> > > > > > On Mon, Jun 03, 2024 at 02:25:01PM +0100, Russell King
> (Oracle) wrote:
> > > > > > > On Mon, Jun 03, 2024 at 08:18:34PM +0800, Sky Huang
> wrote:
> > > > > > > > Add support for internal 2.5Gphy on MT7988. This driver
> will load
> > > > > > > > necessary firmware, add appropriate time delay and
> figure out LED.
> > > > > > > > Also, certain control registers will be set to fix
> link-up issues.
> > > > > > > 
> > > > > > > Based on our previous discussion, it may be worth
> checking in the
> > > > > > > .config_init() method whether phydev->interface is one of
> the
> > > > > > > PHY interface modes that this PHY supports. As I
> understand from one
> > > > > > > of your previous emails, the possibilities are XGMII,
> USXGMII or
> > > > > > > INTERNAL. Thus:
> > > > > > > 
> > > > > > > > +static int mt798x_2p5ge_phy_config_init(struct
> phy_device *phydev)
> > > > > > > > +{
> > > > > > > > +struct pinctrl *pinctrl;
> > > > > > > > +int ret;
> > > > > > > 
> > > > > > > /* Check that the PHY interface type is compatible */
> > > > > > > if (phydev->interface != PHY_INTERFACE_MODE_INTERNAL &&
> > > > > > >     phydev->interface != PHY_INTERFACE_MODE_XGMII &&
> > > > > > >     phydev->interface != PHY_INTERFACE_MODE_USXGMII)
> > > > > > > return -ENODEV;
> > > > > > 
> > > > > > The PHY is built-into the SoC, and as such the connection
> type should
> > > > > > always be "internal". The PHY does not exist as dedicated
> IC, only
> > > > > > as built-in part of the MT7988 SoC.
> > > > > 
> > > > > That's not how it was described to me by Sky.
> > > > > 
> > > > > If what you say is correct, then the implementation of
> > > > > mt798x_2p5ge_phy_get_rate_matching() which checks for
> interface modes
> > > > > other than INTERNAL is not correct. Also it means that
> config_init()
> > > > > should not permit anything but INTERNAL.
> > > > 
> > > > The way the PHY is connected to the MAC *inside the chip* is
> XGMII
> > > > according the MediaTek. So call it "internal" or "xgmii",
> however, up to
> > > > my knowledge it's a fact that there is **only one way** this
> PHY is
> > > > connected and used, and that is being an internal part of the
> MT7988 SoC.
> > > > 
> > > > Imho, as there are no actual XGMII signals exposed anywhere I'd
> use
> > > > "internal" to describe the link between MAC and PHY (which are
> both
> > > > inside the same chip package).
> > > 
> > > I don't care what gets decided about what's acceptable for the
> PHY to
> > > accept, just that it checks for the acceptable modes in
> .config_init()
> > > and the .get_rate_matching() method is not checking for interface
> > > modes that are not permitted.
> > 
> > What I meant to express is that there is no need for such a check,
> also
> > not in config_init. There is only one way and one MAC-side
> interface mode
> > to operate that PHY, so the value will anyway not be considered
> anywhere
> > in the driver.
> 
> No, it matters. With drivers using phylink, the PHY interface mode is
> used in certain circumstances to constrain what the net device can
> do.
> So, it makes sense for new PHY drivers to ensure that the PHY
> interface
> mode is one that they can support, rather than just accepting
> whatever
> is passed to them (which then can lead to maintainability issues for
> subsystems.)
> 
> So, excuse me for disagreeing with you, but I do want to see such a
> check in new PHY drivers.
> 
> -- 
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!

Hi Russell/Daniel,
  IMO, we can check PHY_INTERFACE_MODE_INTERNAL &
PHY_INTERFACE_MODE_XGMII in config_init() or probe(). However,
PHY_INTERFACE_MODE_USXGMII isn't supported by this phy, and
drivers/net/ethernet/mediatek/mtk_eth_path.c uses
PHY_INTERFACE_MODE_USXGMII to switch netsys pcs mux (set
MUX_G2_USXGMII_SEL bit in TOP_MISC_NETSYS_PCS_MUX) so that XFI-MAC can
be connected to external 10Gphy.
  So, basically, for 1st XFI-MAC on mt7988:
- PHY_INTERFACE_MODE_XGMII/PHY_INTERFACE_MODE_INTERNAL: built-in
2.5Gphy
- PHY_INTERFACE_MODE_USXGMII: external 10Gphy

  I add check in config_init():
/* Check if PHY interface type is compatible */
if (phydev->interface != PHY_INTERFACE_MODE_XGMII &&
    phydev->interface != PHY_INTERFACE_MODE_INTERNAL)
	return -ENODEV;

  Also, test with different phy mode in dts:
[PHY_INTERFACE_MODE_USXGMII]
[   18.702102] mtk_soc_eth 15100000.ethernet eth1: mtk_open: could not
attach PHY: -19
root@...nWrt:/# cat /proc/device-tree/soc/ethernet@...00000/mac@...hy-c
onnection-type
usxgmii

[PHY_INTERFACE_MODE_INTERNAL]
[   18.329513] mtk_soc_eth 15100000.ethernet eth1: PHY [mdio-bus:0f]
driver [MediaTek MT7988 2.5GbE PHY] (irq=POLL)
[   18.339708] mtk_soc_eth 15100000.ethernet eth1: configuring for
phy/internal link mode
root@...nWrt:/# cat /proc/device-tree/soc/ethernet@...00000
/mac@...hy-connection-type
internal

Sky

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